1. Field of the Invention
The present invention relates to a flat display panel being a flat display device that displays characters, graphics and images using light emission produced by ionized gas, and particularly to a technique of sealing a structure formed of a front plate and a back plate at the side surfaces thereof.
2. Description of the Prior Art
Conventional flat display panels are referred to as plasma display panels. This type of display panel is disclosed in, for example, Japanese Patent Laid-open Publication No. Hei 2-90192 and Japanese Utility Model Laid-open Publication No. Hei 3-94751. In the structure, two substrates each having plural linear electrodes formed thereon are disposed in parallel so as to confront each other. The linear electrodes formed on one substrate and the linear electrodes formed on the other substrate are disposed in a matrix form. Gas discharges occur at intersections between the linear electrodes on one substrate and the linear electrodes on the other substrate. The gap between the fringe portion of the front plate and the fringe portion of the back plate is sealed with a bonding agent such as a fritted glass. The space between the front plate and the back plate is filled with a discharge gas.
In the conventional flat display panel, voltages are respectively applied to the ends of the linear electrodes leading out of the side end surfaces of the plate. The electrodes arranged on the front plate are formed of a transparent electrode material such as ITO so as to pass through the emitted light produced by a gas discharge. However, the transparent electrode material has a considerably large resistance value because of its low electric conductivity and because of the narrowed and elongated linear electrodes resulting from the trend toward high-resolution and large-sized screens. This causes the problem that as a voltage pulse applied to an end of a linear electrode propagates toward the middle portion of the linear electrode, it is attenuated. For that reason, using current fabrication methods, the conventional flat display is limited up to a screen size of 1 mxc3x971 m.
With recent advances in the information-oriented society, there have been increasing demands for large-sized display screens. As one approach, it has been considered to obtain a large screen by arranging plural prior-art flat display panels side by side.
However, where a large screen is fabricated by arranging plural panels, a large gap between the display regions of neighbor panels causes a large dead space in the screen display, thus resulting in deteriorating the display quality. In order to solve such a problem, it has been considered to reduce the space for sealing the bonding portions between the side surfaces of two plates.
FIG. 1 is a cross sectional view schematically illustrating the end portion in the side sealed structure of a flat display panel disclosed in Japanese Patent Laid-open Publication No. Hei 5-13003. A front plate 11 is formed of a glass substrate 1, and transparent electrodes 2 and transparent dielectric layers 3 formed thereon. A back plate 21 is formed of a glass substrate 4, and metal electrodes 5, black dielectric layers 6 and spacer ribs 7 formed thereon. The front plate 11 and the back plate 21 are arranged in parallel. The open sides of the spaced-plate structure are sealed with a fritted paste.
As described above, the prior-art structure includes the spacer ribs 7 which maintain the gap between the front plate and the back plate to secure a discharge space. The spacer rib 7 is formed of, for example, a porous substance, not suitable for sealing, and is not used to seal the openings between the two plates. The thickness of the spacer rib 7 must be set to a value exceeding the total of the thickness of constituent elements formed on the glass substrate 1 and the thickness of the constituent elements formed on the glass substrate 4. Hence, the spacer rib 7 is formed of, for example, stacked films.
In the conventional flat display panel structure, the front plate and the back plate are spaced widely apart, and the opening area to be sealed with fritted glass 8 becomes large. The fritted glass 8 is in a paste state before its solidification through calcination. The fritted glass 8 is not supported in the opening area for sealing but holds its state by only its viscosity or surface tension against an external force such as gravity. The thickness of the fritted glass is prone to become uneven at the sealing portion. As a result, there has been the problem that the reliability of sealing cannot be secured in the conventional technique. If a large amount of fritted glass is used to avoid such a problem, the area of the front plate on which the fritted glass is rested become large. This means that the dead space cannot be reduced in arranging panels. A large amount of fritted grass contains a large amount of solvent, the large amount of solvent permeating from the opening between a front plate and a back plate will contaminate the discharge space.
In the conventional flat display panel, two transparent insulating substrates are arranged in parallel so as to be spaced apart from each other. Plural linear discharge electrodes are arranged in parallel on each substrate. The linear electrodes on one substrate and the electrodes on the other substrate confront each other and are arranged in a matrix form. A partition wall defining a discharge space for each electrode is formed on the substrate. The display control is performed-by selecting the confronting electrodes arranged in a matrix form. As a result, the display control cannot be independently performed for each display cell. The above-mentioned structure leads to a thick flat display panel.
For that reason, it has been strongly desired to develop a flat display panel with a novel structure different from the conventional structure. The present applicant proposed a flat display panel with a new structure in the international application (PCT/JP98/01444) based on the Patent Cooperation Treaty. In this structure, recessed portions, each acting as a discharge space for a display cell, arranged in a matrix form are formed in the back plate. In the front plate, pairs of cell electrodes are formed on the regions confronting the recessed portions of the back plate. The front plate is disposed over the back plate. In the flat display panel, pin electrodes penetrate the back plate so that a voltage signal can be applied to a given spot of an electrode formed on the front plate. That is, this structure allows a voltage to be applied between a pair of cell electrodes corresponding to a display cell so that the display cells can be respectively display-controlled. Since the back plate has recessed portions each for a discharge space, it is not required to attach or stack partition walls partitioning discharge spaces on the substrate, as shown in the prior art. Hence, this feature allows the display panel to be thinned.
The flat display panel with this new structure differs from the conventional flat display panel using linear electrodes, in that cells can be respectively driven using pin electrodes. In other words, since cells are independently driven, a large screen can be easily divided into plural flat display panels. A large screen can be easily fabricated by arranging panels each smaller than the conventional flat display panel. Additionally, a panel having defect pixels can be easily replaced with a new one.
The objective of the invention is to provide a flat display panel with a novel structure in which the front panel is bonded with the back plate.
Further objective of the invention is to provide a structure that can solve the above-mentioned problems in the conventional flat display panel.
According to the present invention, the flat display panel comprises a front panel of a transparent glass substrate on which cell electrode pairs are arranged for pixels, and a back plate having recessed portions formed in a surface thereof, the recessed portions being positioned so as to confront the cell electrode pairs, the recessed portions each defining a discharge space, the back plate being placed over the front plate; the back plate having a sealing wall having a top surface of the back plate remaining outside a display region formed of the recessed portions; the front plate having a protrusion protruding outward from the outer fringe of the sealing wall; wherein a contact portion between the sealing wall and the front plate is sealed by depositing a bonding agent in a corner portion defined by the outer side surface of the sealing wall and the protrusion of the front plate, the corner portion being adjacent to the bonding portion.
In the flat display panel according to the present invention, at least the front plate or the back plate has a groove extending along the sealing wall in a plate surface region where the top surface of said sealing wall confronts the front plate.
The flat display panel according to the present invention further comprises a barrier for blocking the bonding agent on the outer fringe portion of the front plate.
According to the present invention, a flat panel display comprises a front panel of a transparent glass substrate on which cell electrode pairs are arranged for pixels; and a back plate having recessed portions formed in a surface thereof, the recessed portions being positioned so as to confront the cell electrode pairs, the recessed portions each defining a discharge space, the back plate being placed over the front plate; the back plate having a sealing wall having a top surface of the back plate remaining outside a display region formed of the recessed portions; wherein a contact portion between the sealing wall and the front plate is sealed by means of a bonding agent layer to be bonded on the outer side surface of a superposed structure of the front plate and the back plate as well as a band member to be securely bonded on the outer side surface of the superposed structure pressure-bonded to the bonding agent layer.